Knowledge of a patient's blood pressure is often essential to properly assess the patient's medical condition. Continuous monitoring of the blood pressure enables medical personnel to immediately detect changes in the cardiovascular system indicating stress, and to respond rapidly with the appropriate action. Depending on whether a doctor wishes to monitor arterial or venous pressure, a needle may be inserted into an artery or vein, and a very small diameter tube or catheter run through the needle so that its open end is exposed to the fluid pressure of blood at a desired location in the body. If it is necessary to measure blood pressure in an organ, e.g., inside one of the chambers of the heart, the catheter is simply moved through the blood vessel until it is positioned at the desired location. A sterile solution fills the catheter. The pressure of the cardiovascular system at that point in the body is transmitted through the sterile solution to a fluid pressure sensing device connected to the catheter outside the patient's body. The pressure sensing device typically includes a pressure transducer that produces an electrical signal proportional to the fluid pressure of blood at the open end of the catheter. An analog or digital display, or a cathode ray tube connected to the transducer provides an indication of the patient's blood pressure in response to the electrical signal.
In the past, the pressure sensors used to measure and/or monitor blood pressure have been too expensive to routinely discard after a single use. Instead, the pressure sensors have normally been sterilized for reuse on several patients. The time and labor expense involved in preparing conventional blood pressure sensors for reuse is significant. An increased emphasis on stemming the rising cost of medical treatment has created a demand for low cost disposable pressure sensors.
One such disposable blood pressure sensor is described in U.S. Pat. No. 4,576,181. This pressure sensor includes a shell-like housing in which a pressure transducer is directly mounted, covered by an opaque plate that blocks light from reaching a semiconductor surface of the transducer. The opposite surface of the pressure transducer is mounted over a passage in the housing, providing communication with a fluid-filled catheter. A portion of the passage is filled with a gel which serves to hydraulically couple the fluid pressure to the pressure transducer. Mounted within the housing next to the pressure transducer is a dielectric substrate, including a thick film hybrid temperature compensation circuit with pads on which leads entering the housing through an insulated cable are soldered.
Although the disposable blood pressure sensor described above is substantially less expensive than those reusable sensors previously in use, its material and manufacturing labor costs are significantly more than might be desired. Components such as the thick film hybrid circuit provided on the dielectric substrate mounted adjacent the transducer substantially increase its cost. In addition, the labor required to hand assemble the pressure transducer chip within the housing, and to attach the chip to the hybrid circuit and the hybrid circuit to the cable is significant. The hydraulic pressure coupling gel must be injected through one end of the catheter connector into the passage communicating fluid pressure to the transducer. It is difficult to constrain the gel to the desired passage, because it is injected in the form of a low viscosity liquid having a tendency to run.
In consideration of these problems, the present invention seeks to provide an even lower cost disposable blood pressure transducer than that of the above-described prior art. A further object of this invention is to provide a pressure transducer that may be easily assembled with minimal operations requiring hand labor. Yet a further object is to provide an assembly including a premounted pressure transducer that may be readily interfaced to a fluid pathway and electrical leads. These and other objects and advantages of the present invention will be apparent from the attached drawings and the description of the preferred embodiments that follow.